Please help me with this problem I been stuck in this problem for 45 min and don't know how to go about it ????

3. For the list of numbers {10, 9, 13, 11, 7, 12, 8}, find the average and standard devia- tion. You must do your computation by hand (you can use your calculator to add, subtract, multiply, divide and do powers and roots, but you have to write down what you compute and you cannot use an avg/SD property of a calculator to compute them), and you must show all steps to receive full credit. It is best to organize everything into a table